A single ion trap may be used upstream of an ion mobility separator in order to improve the duty cycle when transferring successive populations of ions into the ion mobility separator. Application of relatively high voltage extraction field is typically required to ensure rapid transfer of ions from the ion trap to the ion mobility separator with minimal dispersion. Application of such a high voltage field can cause heating of the ions, resulting in undesired fragmentation (e.g., of labile compounds). However, slower transfer of ions from the ion trap can lead to a lower duty cycle.
In addition, the ion cloud may not be driven far enough into the ion mobility separator, and may not experience the desired ion mobility separation force during subsequent operation. In this case ions can be lost or remain trapped at the front region of the ion mobility separator.
US2003/0141446 (Blanchard) discloses an ion detecting apparatus and methods.
WO 99/47912 (Spangler) discloses an ion mobility storage trap and method.
U.S. Pat. No. 7,838,826 (Park) discloses an apparatus and method for parallel flow ion mobility spectrometry combined with mass spectrometry.
WO 2014/140579 (Micromass) discloses a coaxial ion guide.
It is desired to provide an improved method of separating ions according to their ion mobility.